During the coming year we will explore the factors responsible for the development of high concentrations of idiotype-specific suppressor T cells. The presence of such cells will be monitored by adoptive transfer experiments and by measuring the capacity of the T cells to form rosettes with autologous red blood cells coated with Fab fragments of antibodies possessing the idiotype (associated with the anti-phenylarsonate antibodies of A/J mice). The factors to be investigated include the requirement for antiidiotypic antibodies, the role of varying dosages of antigen, which has been shown to be required for amplification of suppressor T cells, and the time course of appearance of the idiotype-specific suppressor cells. Efforts will be made to induce such cells by injection of idiotype, rather than antigen, either alone or attached to macrophages. Efforts will be made to isolate an idiotype-specific suppressor T cell factor by sonication of active suppressor cells. Experiments will be carried out to determine whether the T cells which possess receptors specific for idiotype also have Fc receptors. In collaboration with another laboratory, efforts will be made to produce T cell hybridoma cell lines which express the antiidiotypic receptor.